Problem: $10ab + 7ac + 9a - 1 = 9b - 3$ Solve for $a$.
Answer: Combine constant terms on the right. $10ab + 7ac + 9a - {1} = 9b - {3}$ $10ab + 7ac + 9a = 9b - {2}$ Notice that all the terms on the left-hand side of the equation have $a$ in them. $10{a}b + 7{a}c + 9{a} = 9b - 2$ Factor out the $a$ ${a} \cdot \left( 10b + 7c + 9 \right) = 9b - 2$ Isolate the $a$ $a \cdot \left( {10b + 7c + 9} \right) = 9b - 2$ $a = \dfrac{ 9b - 2 }{ {10b + 7c + 9} }$